spacing in double glazing

[Bootneck216]

Can anyone please point me in the direction of where is states in building regulation what the size of the spacing bars in double galzing should be for a house built in 2005

[buildersmate]

It isn't that simple because there are three or four ways of assessing the OVERALL thermal performance of the building, which is what counts. So, for example, it is possible to 'trade' a lower performance in one area against a higher thermal performance in another.
The most common glazing width around 2005 in the UK was 20mm in total on the windows and sidelights and 14mm on glazed doors. This means glazing bars of 12mm wide on the windows and 6mm on the doors (4/12/4 and 4/6/4 respectively). It shouldn't be less, it might be more.